(1) Field of the Invention
This invention relates to a method and apparatus for cooling a preform, in which an injection molded preform is released from an injection mold while the preform is in a heated state, and the preform is then transferred to the other area to cool and solidify it.
(2) Prior Art
In molding of a bottle in which an injection molded preform is cooled and solidified, and the preform is then re-heated later to orientation blow mold it into a bottle-like container, a large amount of preforms are required. Therefore, when a preform is cooled and solified by the injection mold as in conventional injection molding, it takes time for cooling, resulting in a very poor productivity. It has been desired therefore that cooling time is shortened by some means to shorten the molding cycle and improve the productivity of the preform process.
One means has been proposed on the basis of the fact that there is a state where although the interior is in a molten state, the shape of the preform is maintained by a skin layer formed on the surface, and the preform can be released in such a state and immediately transferred to a cooling device at the another position for forced cooling, whereby cooling time of the preform is shortened.
As the cooling means after release, quenching using a refrigerator or contacting with a cooling tube set to a low temperature have been employed.
The cooling by way of a refrigerator poses a problem in that the preform is materially contracted by cooling and this impairs the molding accuracy. On the other hand, in the cooling by way of contact, since the contact with the cooling tube is effected by pressure of air blown into the preform, the wall thickness of the preform becomes thinner than the desired dimension.
The contraction and formation of thinner wall thickness of the preform during the process of cooling do not occur uniformly but the location thereof differs with the injection molding state of the preform. These locations give rise to unevenness of temperature of the preform after being reheated, making it technically difficult to perform orientation blow molding of the preform into a container.